Guys: Is it weird that I dislike his best friend?

I noticed his best friend keeps posting pictures of them together on his profile. When I asked him who was she, he said she is his best friend. He then mentioned they’ve been friends since they were 10 but they ended up having a 5 year relationship. At that point, I didn’t see her as his friend but as his ex and so I couldn’t help but to feel uncomfortable. The fact that she’s saying things like “Happy Birthday love, this was our very first picture and kiss. Miss ya!” makes me uncomfortable, but the fact that he doesn’t say anything about it makes me feel even worse. I’ve been with this guy for about 3 months and so far it was good, but I can’t help but to feel bothered by his “best friend”. So am I off for feeling this way? Any advices and POV you can give me are very well appreciate it!
Guys: Is it weird that I dislike his best friend?
Guys: Is it weird that I dislike his best friend?
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